Batman was invited into entering Sword Art Online (SAO).
The invitation came from someone who hacked the BAT COMPUTER.
At that moment Alfred informed Bruce that a package has arrived and it was a Net Dive Gear with instruction.
He entered SAO to find out who hacked his system not knowing the repercussion, if you die in the game, you die for real.
Mean while, Kirito is searching for Asuna. Someone PM him that Asuna was killed by a man in BAT Costume.
Batman in character and have standard gear
Kirito is Blood Lusted.